Seed for crystal growing



Feb. 27, 1951 s. 1. SLAWSON SEED FOR CRYSTAL GROWING Filed June 8, 1948 N O S W A L S IN VEN TOR. STEWART I.

ATTOR NEY Patented Feb. 27, 1951 SEED-FOR. CRYSTAL GROWING Stewart I. Slawson, Lorton; Va.

AnnlicatiomJunefi, 1948; Serial,No; 31,77fi

13 Claims, Cl.v.171"--327 (Granted: under. the. act of; March 3,.18183, as,

amended April; 30, 1928; 370 0.-G. 757) This invention relates-to crystal-growthand in particular to a type of seed crystal and the method of production thereof.

The general object of the invention is'to-provide a seed crystal Whichwill promote-a relatively rapid crystal growth f rom a crystallizin g solution.

Itis also anobieet of theinvention-to provide a seed crystal which will promote the growth of i a crystal having-'2), maximum :.of cleanbar stock.

It is a further obj cot oi the invention to pro vide a seed'scrystalhaving a relatively short: dimension parallel to the longitudinal axis of the crystal-to be grown.

It isan additional object 'ofthe invention to provide aseed crystal which-may 'hec-utfrom thestocli of the crystalgrownthereon and which, by. regrinding of the-cap, surfaces, may be reused.

The attainment of these objectives and others such as the provision oi seed "crystals with aminimum of wastage; of:' material: will: be apparent from" the following description and from the drawings. hereto appended both offwh-ich are merely. illustrative and'iare not liinitative' beyond the scope as defined by the-herewith: appended claims-.. 7

Incthese drawings:

Figure 1 is an isometricyiewof a seed crystal formed in accordance with the-applicantsinventime.

Figure 2vis anisometric viewof-a seedcrystal produced in accordance with conventional practice; and

Figure 3 is an=isometricview oiacrystalsuch as ammonium dihydrogen phosphate grown ona seed crystal of the applicant.

In=tlieart of growing crystals of' various salts it is the general-practice to growtthese crystals on" seeds. These seeds-generally consist ofrectangular plates ofthe crystallii'ie material cut from the bar stock of acrystalof the-material-at right angles to the longitudinal axis ofthe-crystal, i. 6;: the Z axis. Theseedplatemay: be originally: cut from thecrystal bar stock by cutting the latter at: angles of fortyeirvede-grees to its-X' and Y-'axes and'ithe-ncutting a seed plate therefromperpendicularly to:the Z 'a-Xis. A pluralitytof seed plates so cutarethenmounted in theusualicrystal growing containers-inwhich is the crystallizingsolution of the desired salt;

Crystalllzationotthe salt-Lon theseed platesiorms 1 cap surfaces on the seed plates which atfirst may he opaque and more on leSsirreguIar; soon as the. seed forms completely regular crystal faces the operation is stoppedand theperfect seedsaare sortedfifromthe defectively formed ma terial. This initial growing: operation. requires from-ten-totw-enty days.v The perfect seeds-are then mounted in the containersof the crystalliz ing solution and crystal growth proceeds: until crystalsof the desired-size are grown; Ingrowth from-a plate this step: is necessaryv in order to are rive at a seed which combine;th-eoptimumcomihination: of edges and; surfaces: ion'subsequent crystal growth.

In contrast to this method: of preparing seed crystals" the, applicant recogn'mesr the; advantage of; providing this. bestcombinationof surfaces edges and cuts a ,b-loclr ofimateriahout ofithe bar; stock of: a crystal atright anglesto they 2" axis there-oil He then: cuts orcgrinds; cap faces on this block approximately: parallel tothe: cap faces of the crystal.- The; cap; faces-areslightly rough due tothemethodof. grinding-orrcutting them. They may'vary as=much asrplus-orminus five degrees from true parallelism with the cap faces :as, grow-n, In the dimension ass measured along the Z'axis these out seedicrystalsam fromone-halfto-two and one-haltinchcs shorter. than the seed crystalson which the. cap faces are grown. as above. described Referring to the drawings, Figure 1 show-ea med crystal for: ammoniumdihydrogen phosphate prepared in accordance with the applie cants method. This.- seedcrystal comprises a polyhedron having twelve surfacesoni eight of which (the cap v surfaces) the coming outof solution deposit; The seed as shown: comprises a-body portion it ontheslateralfaces of which the cap faces 12, H3, i6, [8, 20, 22, 24 andlzfifare cut. Thesecap faces; due to the manner of cwting them, are-notperfectly-srnooth: Theyare scored.- with minuteridaea and valleys V which, afford. a large-number ct microscopioed es and corners onwhichthe ionszcoming outofsolutioncan form andbuild. They: therefore -.induce growth, at lower degree of super-saturation and with a minimum formation of veils.

Figure 2 shows a seed crystal on. which cans such as 40" and Marc grownon a seed plate 30'. These cap surfaces grow on the faces of theseed plate which are perpendicular to the longitudinal axis of the original crystal from whichthe plate was cut. These cap faces growanddevelop as the ions precipitating from-solution pileup at the corners of the seed plate and along the edges thereof; Rough and irregular surfaces; parallel to the cap faces, gradually form. The crystallized material thus far precipitated is opaque-due to the heterogeneous orientation of the ions. Gradually the precipitated materialencloses the poor quality growth parallel to the Z axis and when the cap faces are completely formed the end point of the seed growth is reached. The cap faces, as developed, are very smooth and regular and when the seed is used for further crystal growth 'there is a considerable formation of veils in the vicinity of these developed cap faces. The dimension of the seed crystal along the Z axis is therefore much greater than the completely ground seed crystal of the applicant.

Figure 3 is an isometric drawing of a crystal of ammonium dihydrogen phosphate grown on one of the applicants seed crystals. In this figure body ll] of the seed crystal is indicated. Ground cap faces 20, 22, 24 and 26 are also indicated. The grown crystal is indicated generally at 68. There are no veils in the vicinity of the ground cap faces apparent, and the crystal is composed largely of clear transparent stock. The relative proportion of this clear stock in the grown crystal is much greater when the applicants ground seed crystal is used than when a seed crystal of the type shown by Figure 2 is used.

The applicant has found that he can grow crystals of a wide range in composition by the use of his particularly ground seed crystal. Among the other crystallizable materials are, ammonium phosphate, ammonium arsenate, potassium phosphate, potassium arsenate, ammonium iodate, lithium sodium sulphate, lithium sulphate, magnesium sulphate, ammonium potassium thiosulphate, barium thiosulphate, potassium tungstate, lanthanum sulphate, triethyl ammonium nitrate, sodium divanadate tetrahydrate, benzil, hexachlorobenzene, N-chlorophthalimid, pentabromethane and para-nitroacetanilid. All of these compounds develop caps in crystalization.

In general each salt requires a capped seed crystal on which the arrangement of the cap faces is peculiar to the particular salt being crystallized. Thus a quartz seed will be hexagonal in transverse section and there will be six cap faces on either side of the body part which (faces) will have a particular angular relationship to each other and with respect to the Z axis of the seed.

The advantages which inhere to the applicants method of crystal growth are:

1. Because of the shorter length of the applicants seed along the Z axis it is of a less volume as compared to the grown seed. More of his seeds can be mounted in a container of a definite volume and more crystals therefore are grown in a run.

2. Because of the relative roughness of the ground surfaces crystallization takes place at a lower super-saturation which reduces the tendency to flaw than with the surfaced grown seeds.

3. Because the ground surfaces remain sharply defined in the grown crystal and because of the lack of veils in the vicinity of the ground surfaces, the seed crystal can be reground and reused. This is not possible when grown seeds are used, because of the small area of the clear crystal growth in the region near the original plate.

4. Elimination of the loss of caps due to a small amount of resolution.

5. Elimination of the seed growing step. As stated above this generally requires from to days. The crystal growing apparatus is thereby available for the continual growth of crystal material.

6. The yield of perfect crystals is much higher 4 with the applicants ground seeds than with the grown seeds.

7. The yield of usable material is much higher per crystal and there is a corresponding reduction in the amount of waste material per crystal.

While the foregoing description has been limited to the growing of crystals of ammonium dihydrogen phosphate on a seed crystal having ground cap faces, it is not desired to be closely restricted thereto since as above indicated the applicant has grown crystals of many different compositions on seeds having cap faces ground thereon peculiar to the arrangement of the cap faces of the particular material being crystallized. Such variations would be apparent to one skilled in the art and are intended to be included within the scope of the invention to the extent defined by the herewith appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor.

What is claimed is:

1. The method of making capped seed crystals for promoting the relatively rapid growth of crystals in a crystallizing solution comprising cutting a block of material from the bar stock of a crystal of the type developing capped ends, said block out from said bar stock at right angles to the Z axis of said crystal, and grinding cap faces approximately parallel to the cap faces of the crystal to be grown on the sides of the block extending at right angles to said Z axis.

2. The method of making capped seed crystals for promoting the relatively rapid growth of ammonium dihydrogen phosphate crystals from a crystallizing solution thereof, comprising cutting a block of material from the bar stock of a crystal of ammonium dihydrogen phosphate at right angles to the Z axis of said crystal and grinding cap faces approximately parallel to the cap faces of the ammonium dihydrogen phosphate crystal to be grown on the sides of the block extending at right angles to said Z axis.

3. The method of making capped seed crystals for promoting the relatively rapid growth of iodic acid crystals from a crystallizing solution thereof, comprising cutting a block of material from the bar stock of a crystal of iodic acid at right angles to the Z axis of said crystal and grinding cap faces approximately parallel to the cap faces of the iodic acid crystal to be grown on the sides of the block extending at right angles to said Z axis.

4. The method of making capped seed crystals for promoting the relatively rapid growth of quartz from a crystallizing solution thereof comprising cutting a block of material from the bar stock of a crystal of quartz at right angles to the Z axis of said crystal and grinding cap faces approximately parallel to the cap faces of the quartz crystal to be grown on the sides of the block extending at right angles to said Z axis.

5. In the method of growing crystals on seed crystals from a crystallization solution the step of mounting in said solution seed crystals having ground cap faces approximately parallel to the cap faces of the crystal to be grown.

6. A capped seed crystal for promoting the relatively rapid growth of a crystal by crystallization from a crystallizing solution comprising a polyhedral block of the material to be crystallized having crystallizing surfaces, and cap surfaces ground on said block extending approximately to said crystallizing surfaces and substantially parallel to the cap surfaces of the crystal to be grown. V

7. A method for the dry preparation of capped seed crystals of a minimum size from a minimum quantity of material comprising, cutting a block of material from bar stock of a crystal of the type to be seeded} and-grinding faces on said block at angles with the direction of crystal growth substantially equal to the angles which the respective natural cap faces of the potential crystal will form with said direction.

8. A method of dry preparation of capped, rapid-growing seed crystals of a minimum size from a minimum quantity of material, comprising, cutting a block of seed material from bar stock of a crystal 'of the type to be seeded, the direction-of-desired-crystal-growth dimension of said block being just large enough with respect to the dimensions normal thereto and with respect to the angle which cap faces naturally form therewith to permit full, symmetrical development of said cap, faces, and grinding cap faces on said block at angles with the said direction of growth substantially equal to the angles which cap faces naturally form therewith.

9. The method of treating a cap face of a seed crystal to increase the rate of crystal growth from solution thereon and to substantially reduce the distance from said seed crystal cap face into the resulting grown crystal in which imperfect grown material occurs, comprising, reducing the lower limit of supersaturation at which crystallization will occur by roughening the surface of said cap faces.

10. A method for the large-scale, continuous production of grown bar crystals having a minimum proportion of waste material comprising, preparing v at-seed crystal according to the method of claim'BLgrowing a crystal bar thereon by conventional processes said crystal having as waste material only that center portion thereof corresponding to the length of the seed crystal, and repeating the cycle by cutting from said grown crystal bar a block of said center portion and regrinding cap faces thereon according to the method of claim 8.

11. A compact, capped seed crystal for the growing of crystal bars comprising a polyhedral block of material to be crystallized wherein approximately all of the surface area of the block consists in ground cap faces which form angles with-the direction of crystal growth substantially equal to the angles which natural, grown cap faces form therewith.

12 A seed crystal as defined in claim 11 havingroughened cap faces.

1 3;-A capped seed crystal for the growing of crystal bars comprising a polyhedral block of material to be crystallized having roughened cap faces which form angles with the direction of crystal growth substantially equal to the angles which natural grown cap faces form therewith.

STEWART I. SLAWSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 5 Re; 19,697 Kjell-gren Sept. 10, 1935 2,424,273 Haas, Jr July 22, 1947 2,442,755 Christensen June 8. 1948 

